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Date:   Fri, 20 May 2022 01:07:07 +0000
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Subject: Re: [PATCH 1/4] memcg: enable accounting for large allocations in mem_cgroup_css_alloc
From:   Shakeel Butt <shakeelb@google.com>
To:     Vasily Averin <vvs@openvz.org>
Cc:     Roman Gushchin <roman.gushchin@linux.dev>,
        "Michal =?utf-8?Q?Koutn=C3=BD?=" <mkoutny@suse.com>,
        kernel@openvz.org, linux-kernel@vger.kernel.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>, cgroups@vger.kernel.org
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On Fri, May 13, 2022 at 06:51:41PM +0300, Vasily Averin wrote:
> cgroup mkdir can be misused inside memcg limited container. It can allocate
> a lot of host memory without memcg accounting, cause global memory shortage
> and force OOM to kill random host process.
> 
> Below [1] is result of mkdir /sys/fs/cgroup/test tracing on VM with 4 cpus
> 
> number	bytes	$1*$2	sum	note	call_site
> of	alloc
> allocs
> ------------------------------------------------------------
> 1       14448   14448   14448   =       percpu_alloc_percpu:
> 1       8192    8192    22640           (mem_cgroup_css_alloc+0x54)
> 49      128     6272    28912           (__kernfs_new_node+0x4e)
> 49      96      4704    33616           (simple_xattr_alloc+0x2c)
> 49      88      4312    37928           (__kernfs_iattrs+0x56)
> 1       4096    4096    42024           (cgroup_mkdir+0xc7)
> 1       3840    3840    45864   =       percpu_alloc_percpu:
> 4       512     2048    47912           (alloc_fair_sched_group+0x166)
> 4       512     2048    49960           (alloc_fair_sched_group+0x139)
> 1       2048    2048    52008           (mem_cgroup_css_alloc+0x109)
> 	[smaller objects skipped]
> ---
> Total			61728
> 
> '=' --  accounted allocations
> 
> This patch enabled accounting for one of the main memory hogs in this
> experiment: allocation which are called inside mem_cgroup_css_alloc()
> 
> Signed-off-by: Vasily Averin <vvs@openvz.org>
> Link: [1] https://lore.kernel.org/all/1aa4cd22-fcb6-0e8d-a1c6-23661d618864@openvz.org/
> 

Acked-by: Shakeel Butt <shakeelb@google.com>